This invention relates to a power steering system for watercraft and, more particularly, to an improved power steering system which facilitates manual control of the watercraft steering without interference from the power steering system.
It is well-known with marine outboard drives, particularly those employing large displacements, to employ a hydraulic power steering system for assisting the operator in steering the watercraft. These systems include a hydraulic cylinder that is connected to the tiller or steering mechanism of the marine outboard drive and which is energized in response to operator control so as to effect power steering of the outboard drive.
These systems are very desirable in that the steering forces for large outboard drives can be quite large and non-assisted steering can, at times, be difficult. However, when a power steering system of the type described is employed, then it is difficult for the operator to manually position the outboard drive. There are times when manual positioning of the outboard drive may be desirable either when the power steering system becomes somehow defective, for servicing or other reasons. However, because of the connection of the hydraulic motor to the steering mechanism for the outboard drive, the operator must manually force the fluid through the hydraulic system in order to effect manual steering. This is obviously a disadvantage.
Although the arrangement may permit disconnection of the hydraulic cylinder or motor from the tiller, this is a cumbersome activity and then requires reinstallation which is not at all desirable.
These problems can be best understood by reference to FIGS. 1-3 of the drawings which show, respectively, a marine outboard drive attached to the transom of a watercraft; a perspective view showing the hydraulically assisted steering mechanism and a hydraulic circuit diagram for the conventional prior art type of construction.
Referring first to FIGS. 1 and 2, an outboard motor that is steered in accordance with both the prior art constructions and which may be steered in accordance with an arrangement employing one of the embodiments of this invention is identified generally by the reference numeral 11. Although the description relates to an outboard motor, it is to be understood by those skilled in the art that both the prior art type of systems and systems embodying the invention may be employed with other types of marine outboard drive such as the outboard drive unit of an inboard/outboard drive. Thus, the term outboard drive, as employed herein, is intended to encompass either the outboard drive portion of such an inboard/outboard drive or an outboard motor per se.
The outboard motor 11 includes a power head, indicated generally by the reference numeral 12 which is comprised of a powering internal combustion engine of any known type and a surrounding protecting cowling. As is typical with outboard motor practice, the driving internal combustion engine is supported so that its output shaft rotates about a vertically extending axis and drives a drive shaft (not shown) rotatably journalled within a drive shaft housing 13 which depends from the power head 12. The drive shaft housing 13 terminates in a lower unit 14 that contains a conventional forward neutral reverse transmission for driving a propulsion device such as a propeller 15 in a manner well-known in this art.
A steering shaft 16 (FIG. 2) is affixed to the drive shaft housing 13 in any known manner and is journalled for steering movement about a generally vertically extending steering axis within a swivel bracket 17. A tiller 18 is affixed to the upper end of the steering shaft 16 and extends forwardly across the transom 19 of an associated watercraft 21 for steering movement in a manner which will be described.
The swivel bracket 17 is connected by means of a horizontally extending tilt pin 22 to a clamping bracket 23 that is affixed to the transom of the associated watercraft in a well-known manner. This pivotal connection permits tilt and trim movement of the outboard motor 11.
This tilt and trim movement may be controlled hydraulically by means of a tilt cylinder 24 that is connected between the clamping bracket 23 and the swivel bracket 17 and a trim cylinder 25 that is carried by the clamping bracket 23 and which has a piston that engages the swivel bracket 17. This type of hydraulic tilt and trim control is well-known in the art as is the remainder of the construction of the outboard motor 11. Since the invention deals primarily with the steering mechanism, further description of the details of the outboard motor 11 are not believed to be necessary to understand the invention or the disadvantages of the prior art.
The steering mechanism will now be described again by reference primarily to FIGS. 1 and 2, although most of the details of the steering mechanism appear in FIG. 2 wherein the steering mechanism is shown in perspective view. This steering mechanism includes a steering control such as a steering wheel 26 that is mounted in the hull 21 forwardly of the transom 19 in a known manner. The steering wheel 26 is affixed to at a pinion gear 27 that is enmeshed with a rack 28 slidably supported within a housing 29.
One end of a wire bowden wire transmitter 31 is connected to the rack 28 and is surrounded by a protective sheathing. The other end of the wire actuator is mounted within a support tube 32 and has a rod or piston 33 affixed to its outer end which is connected to a mechanism, indicated generally by the reference numeral 34 for transmitting steering movement from the steering wheel 26 to the tiller 18. This mechanism includes a cross bar 35 that is pivoted to one end of the rod 33 and which is pivotally connected, by means of a pivot pin 36 to a steering arm 37. The other end of the steering arm 37 is connected to the tiller 18 by a connector 38.
The mechanism for steering further includes a hydraulic assist that includes a hydraulic cylinder 39 having a piston, to be described, that has a piston rod 41 affixed to one end and which is connected to the cross bar 35 for actuating it. A control valve assembly 42 is also mounted on the cylinder 39 and is actuated in response to steering imputs from the wire actuator 31 in a manner as described in the copending application entitled "Steering System for Marine Propulsion Unit," Ser. No. 08/014,650, filed Feb. 8, 1993 in the name of Eiichiro Tsujii and Akihiro Onoue, which application is assigned to the assignee hereof now issued as U.S. Letters Pat. No. 5,330,375. The disclosure of that reference is incorporated herein by reference.
The prior art type of hydraulic circuitry by which the fluid motor 39 is energized may be best understood by reference to FIG. 3, which is a schematic hydraulic diagram. It will be seen that the fluid motor 39 is comprised of a cylinder 43 that defines a cylinder bore 44 in which the aforenoted piston 45 is slidably supported. The piston 45 is, as noted, connected to the piston rod 41. The piston 45 divides the cylinder bore 44 into a pair of fluid chambers 46 and 47 with the piston rod 41 extending through the chamber 47.
The control valve 42 is depicted as being of a three-position two-way valve and is shown in its neutral position in FIG. 3. In this condition, conduits 48 and 49 which extend to the chambers 46 and 47, respectively, are closed off.
The system further includes a remotely positioned fluid power source that includes a reservoir 51 in which hydraulic fluid is contained and which is drawn through a conduit 52 by a pump 53. The pump 53 is driven by an electric motor 54 and discharges fluid under pressure to a supply port 55 in which a check valve 56 is provided. This check valved port 55 communicates with a first port 57 of the valve 42.
A return conduit 58 is provided in the supply port 55 and a pressure relief valve 59 is positioned in this line so as to limit the amount of pressure build-up in the port 55 by bypassing fluid back to the reservoir 51.
The valve 42 also has a return port 61 that communicates with the reservoir 51 through a return line 52.
The control valve 42 is shifted from the neutral position shown in FIG. 3 to either a right-hand or left-hand steering position depending upon the steering inputs by the steering wheel 26. When the valve 42 is shifted to the right as seen in FIG. 3, the port 57 communicates with the conduit 48 and the fluid motor chamber 46 is pressurized. At the same time, the chamber 47 is connected to the return line 62 by the valve 42 so that fluid can be displaced from the chamber 47 back to the reservoir 51. Since the piston rod 41 extends through the chamber 47, more fluid will be required to fill the chamber 46 and it is displaced from the chamber 47 and this make-up fluid is drawn from the reservoir 51 as is well-known. When the piston rod 41 is moved to the right, the outboard motor 11 will be pivoted in a counter-clockwise direction and will effect the steering of the associated watercraft to the right.
When left-hand steering is called for, the valve 42 is moved in the opposite direction so that the line 49 is pressurized and the line 48 is the return line. Fluid then fills the chamber 47 and is displaced from the chamber 46 to cause the piston 45 to move to the left as shown in FIG. 3.
It should be readily apparent from a review of FIG. 3 that although hydraulic-assisted steering is possible, if the operator wishes to manually steer the outboard motor 11 either by pushing on the tiller 18 or the outboard motor 11 itself, the fluid motor 39 will act as a hydraulic lock against such movement. As a result, manual steering is difficult if not impossible.
It is, therefore, a principal object of this invention to provide an improved arrangement for a hydraulically steered outboard drive wherein manual steering can be accomplished if desired.
It is a further object of this invention to provide an arrangement wherein a hydraulic steering mechanism for a marine outboard drive may be manually bypassed to permit manual steering movement of the outboard drive.